1. Field of the Invention
The present invention relates to electrical characteristic testing of a semiconductor device, such as a BGA (Ball Grid Array), a CSP (Chip Size Package), a WLCSP (Wafer Level Chip Size Package) or a flip chip, which has a ball-shaped external terminal.
2. Description of the Prior Art
Heretofore, a Kelvin contact measurement has been known as a technique for testing electrical characteristics with a high degree of accuracy. The Kelvin contact measurement is performed under a condition that two contactors connected to respective ones of a sense terminal and a force terminal of a measuring apparatus are in contact with one external electrode of a semiconductor device (i.e., Kelvin contacts). The Kelvin contact measurement is capable of cancelling influences of a contact resistance and a residual resistance of a measurement cable to provide extremely high measurement accuracy.
In an operation of testing a semiconductor device based on the Kelvin contact measurement, a cantilever-type contactor is commonly used. FIG. 1 shows the structure of a conventional cantilever-type contactor. As shown in FIG. 1, the cantilever-type contactor 11 has a beam portion 11a and a probe portion 11b. The contactor 11 is supported by a support plate of a probe card or the like, through one end of the beam portion 11a. The support plate is adapted to be moved in an upward/downward direction in such a manner as to allow the probe portion 11b to be brought into contact with an external electrode of the semiconductor device in conjunction with the movement so as to measure electrical characteristics of the semiconductor device. A testing method based on the Kelvin contact measurement using such a cantilever-type contactor is disclosed, for example, in JP 2003-270267A.
The cantilever-type contactor has a feature of being able to facilitate a wiping operation. Specifically, an oxide film or a contaminant is likely to be formed or attach on a surface of the external electrode (made of metal) and intervene between the contactor and the external electrode, to cause difficulty in accurately performing the measurement if nothing is done. Thus, it is critical to perform the wiping operation, i.e., an operation of removing the intervening substance, such as an oxide film, from the surface of the external electrode, so as to expose the original metal surface of the external electrode, in advance of the measurement.
Recent years, along with complexification in configuration of a semiconductor device for meeting needs for higher-speed operation and larger capacity, a semiconductor device (e.g., BGA or CSP) having a ball-shaped external electrode (hereinafter referred to as “bump ball”), instead of conventional types, such as a lead terminal and an electrode pad, has been increasingly used. If such a semiconductor device having a bump ball is subjected to the testing method using the above conventional cantilever-type contactor, the following problems will occur.
FIG. 2 is a schematic diagram showing a contact state between the conventional cantilever-type contactor and one bump ball. As shown in FIG. 2, the conventional cantilever-type contactor 11 has a tip end P which is fairly thinner and weaker than the bump ball 13. Specifically, the bump ball 13 has a diameter of about 100 μm, whereas the tip end P of the cantilever-type contactor 11 typically has a thickness of about 10 to 50 μm. Thus, during a process of bringing the cantilever-type contactor 11 into contact with the bump ball 13, the tip end P is likely to be deformed. In some cases, the tip end P slips off a surface of the bump ball 13 to preclude a stable contact with the bump ball 13. In some cases, the tip end P deeply sticks into the bump ball 13 to seriously damage the bump ball 13. Considering these problems, it is difficult to use the conventional cantilever-type contactor for testing of a semiconductor device having a bump ball.
For this reason, a POGO pin-type contactor has been used mainly in the electrical characteristic testing of a semiconductor device having a bump ball. FIG. 3 shows a testing method using a typical POGO pin-type contactor. The POGO pin-type contactor illustrated in FIG. 3 comprises a plunger 26 and a body member 27. A coil spring 28 is arranged inside the body member 27 in such a manner as to allow the plunger 26 to be brought into contact with one bump ball 23, with a spring load depending on elongation or contraction of the coil spring 28, and electrically connected to the bump ball 23.
However, it is hard to perform the wiping operation using the POGO pin-type contactor illustrated in FIG. 3, and thereby it is difficult to achieve a high-accuracy measurement. Moreover, dusts are likely to be trapped in notches or depressions in a measurement portion (indicated by an elliptic area in FIG. 3) of the plunger 26, and the trapped dusts are hardly removed from the depressions. The difficulty in removing the dusts is likely to cause the occurrence of defects, such as contact failure, and preclude long-term use of the contactor. In addition, in connection with recent progress in integration of a semiconductor device, a bump ball has been increasingly reduced in size. Thus, in an operation of testing electrical characteristics of a semiconductor device having such a small-sized bump ball based on the Kelvin contact measurement, it is extremely difficult to allow two POGO pin-type contactors to be brought into contact with one bump ball. This makes it difficult for the POGO pin-type contactor to achieve a high-accuracy measurement in a simple manner.